The removal of paint from large objects such as airplanes and the like poses inherent dangers to the workers involved, as well as to the surrounding environment. Generally, the surfaces of the airplane are sprayed with paint remover (stripper) in a maintenance hangar with large fans employed to drive away, or at least reduce the concentration of, toxic fumes generated during the stripping operation. Although the workers involved in the paint removal operation typically wear protective clothing such as gloves and gas masks, workers in other areas of the hangar working on other jobs are usually not so protected and are placed at risk by exposure to the contaminated fumes.
Further, in such stripping operations, liquid paint remover is generally allowed to run onto the floor, not only posing health risks to the workers in the hangar, but also to the surrounding land and ground water from run-off and drainage. Additionally, such spent liquid paint remover becomes sticky with the components of stripped paint dissolved therein. Thus, the job of removing paint from airplanes generally involves two jobs, stripping of the paint from the airplane and then clean-up of the spent paint remover from the hangar floor, both of which pose serious health risks to the workers involved.
One example of a prior art device for the removal of surface coatings such as paint from the surfaces of large objects is disclosed in U.S. Pat. No. 1,842,099 to Johnson which describes a portable unit with a series of lines for pumping a heated solvent into a pipe network surrounding the object to be treated, such pipes including perforations for spraying the hot cleanser onto the object. Gutters are positioned at lower edges of the object for receiving spent solvent. Drainage pipes and lines return the liquid solvent to the portable unit where it is filtered, and then reheated and once again pumped onto the object being treated.
U.S. Pat. No. 1,608,635 to Theriot discloses a similar portable apparatus for removing paint wherein a stripping solution is heated and pumped into a discharge line for spraying onto the object to be stripped with such object being placed on an inclined platform having a gutter leading therefrom which returns spent solvent to a receiving tank on the portable unit.
U.S. Pat. No. 2,419,397 to Frohoff et al. discloses a stationary spraying rack for railway cars. Such rack generally forms a housing having a track running therethrough such that the railway car may be positioned therein and sprayed down with hot alkaline solution. The spent cleaning solution is then drained from the floor of the rack and delivered to a reconditioning tank. Similarly, the more recent U.S. Pat. No. 4,378,755 to Magnusson et al. discloses a stationary housing for de-icing and cleaning airplanes. The airplane to be cleaned is slowly taxied through the housing wherein it is sprayed with a de-icing or cleaning solution. The spent solution is removed by draining ducts formed in the floor of the housing and collected in a tank for subsequent purification.
Generally, early prior art patents directed to methods for stripping paint from objects have employed heating a stripping solution. While some present day paint solvents are heated for use, others are employed at room temperatures. The primary component of many popular paint strippers, methylene chloride, has a boiling point of 40.degree. C. or 106.degree. F. and is generally used at room temperatures. Such low boiling point, coupled with a correspondingly high vapor pressure, accounts for the contaminating fumes common to paint stripping operations which, as discussed above, endanger not only the workers involved but also others in the area. And, paint strippers which are heated for use, although liquid at room temperature, similarly form noxious fumes upon heating to stripping temperatures. However, such fumes are often readily dispersed. But, because methylene chloride vapor is heavier than air, the fumes generated thereby are not readily dispersed, but rather tend to remain low, being trapped by the air.
Examples of portable units known for use in removing coatings from airplanes are U.S. Pat. No. 2,733,723 to Whitcomb and U.S. Pat. No. 4,146,044 to Dow, both of which are directed to cleaning the inner surfaces of airplane fuel tanks and do not address the problems of removing paint or grease from the large exterior surfaces of the airplane. Such task is generally performed by spraying such surfaces in a hangar with the fumes dispersed by fans and the spent liquid solvent collected on the hangar floor for subsequent clean up. Although it is generally known to provide troughs or gutters under the airplane edges to catch the liquid solvent which drips therefrom, thereby facilitating the clean-up phase of the stripping job, there is no known prior art method for trapping or containing the hazardous solvent fumes generated during stripping. Further, there is no known prior art method for collecting and re-processing such fumes for subsequent re-use as a solvent.